A disadvantage of nylon 6 (poly(.epsilon.-caprolactam)) yarns is that they have a high acid dye rate that is further increased when the yarns are dyed in hot dyeing processes. This high dye strike rate makes it difficult to achieve uniform dyeing of substrates comprised of nylon 6 yarns. In many of the continuous dyeing processes used today, such as Kusters, print, spray, and fluid dyeing, the dye is applied directly to the fabric at high concentration and is rapidly fixed. There is little opportunity for dye leveling to occur as it would in a beck process.
A further disadvantage of nylon 6 yarns that results from their high dye strike rate is that they are more readily stained by various foodstuffs containing acid dyes than similar yarns made of nylon 6,6 (poly(hexamethylene adipamide)). This is true whether the yarn has been dyed by conventional dyeing processes or is undyed, e.g., either a "white" yarn or a "producer-colored" yarn which is not dyed, but colored by the addition of colored pigments to the polymer prior to spinning. For this reason, it is more difficult to eliminate staining of both dyed and undyed nylon 6 substrates, such as carpets or other textiles, by the application of stain-resist agents.
The present invention overcomes the above disadvantages by providing a means for producing nylon 6/6,6 melt-blended yarns having reduced acid dye rates, both when the yarn is undyed, but especially after dyeing. In particular a greater than expected reduction in acid dye rate is achieved upon application of a stainblocker to the yarns. This results in both dyed and undyed products comprised of these yarns which have superior stain-resistance as compared to that of products comprised of comparable nylon 6 homopolymer yarns and equivalent at some compositions to nylon 6,6 yarns which have been treated with a stain-resist agent.